President Donald Trump says his administration is encouraging many Americans to wear face masks in public, though he stresses that the recommendation is optional and is conceding that he will not be complying with it.

The new guidance is raising concern that it could lead to a sudden run on masks.

Some in the U.S. already have begun acquiring or creating face masks of their own even before this week.

But the administration’s new guidance is expected to apply to people in areas of the country hit hard by the coronavirus and is likely to test the market’s ability to accommodate a surge in demand.